The present invention relates to a core sampler, particularly in the field of oil prospecting, comprising:
a core-sampling ring, PA1 an outer barrel for rotating the sampling ring, and PA1 an inner barrel which has a free front end element and is intended to accommodate a core sample during sampling, the inner and outer barrels being more or less coaxial, and PA1 a surface of revolution of the free end element, on the same side of the ring, designed to interact with an internal surface of the latter, or, if appropriate, of the outer barrel, so as together to set a predetermined passage for core-sampling fluid.
In the case of a core-sampler of this kind, the free end element of the inner barrel has a circular lip parallel to the longitudinal axis of rotation and situated in an annular housing in the ring, which also extends parallel to the longitudinal axis of rotation. Regulating the passage for fluid herein proves tricky, for example given that the inner barrel is fixed to the outer barrel a great distance away from the position of this passage and given the significant variations in length which may occur in a core sampler on account of the variable and high temperatures that the latter may experience during sampling. To date, the operator assembling a core sampler tries to obtain a correct setting of this passage by taking account of the differences in length exhibited by the various portions of the inner and outer barrels, and by taking account of the temperatures which it is assumed are reached during core sampling. It is, however, known that in practice the passage actually obtained may be too different from the one anticipated. Furthermore, the inner barrel may be made of a different material (for example glass fibre coated with a binder) from that of the outer barrel, which is usually made of steel, and the differential expansions that these two barrels undergo oppose the obtaining and/or maintaining of the desired setting for the fluid passage. Furthermore, a core sample entering the inner barrel may push the latter slightly towards the top of the outer barrel, depending on the play in the thrust ball bearings or ball bearings which connect the inner and outer barrels, and this may change the aforementioned setting appreciably.
In either event, poor setting of the said passage may lead, for example, to an excessive flow rate of sampling fluid towards the core sample and to a possibly deep adverse alteration thereof by washing, etc., or may, for example, lead to excessive contact between the said surface of revolution of the free end element and the internal surface of the ring or of the outer barrel, leading to seizure of these surfaces as one rotates with respect to the other, or to deformation and/or breakage of the free end element, etc.
The object of the present invention is to overcome the aforementioned drawbacks, and others which are not explained hereinabove but are known to those skilled in the art, and to provide a means that makes it possible simply and reliably to obtain the correct regulation, even regulation down to zero or almost zero passage for the core-sampling fluid between the free end element of the inner barrel and the corresponding internal bearing surface, without troublesome pressure of one on the other, and therefore without the aforementioned risks of seizure, deformation or breakage at this point.
To this end, according to the present invention, the free end element is mounted in the core sampler in such a way that it can slide coaxially over an end portion of the inner barrel, between a position in which the surface of revolution is in contact with the internal surface of the ring or of the outer barrel, respectively, and an extreme position away from this internal surface.
In one embodiment of the invention, the sliding free end element and the end portion each comprise a stop, which stops interact with one another when the inner barrel is withdrawn from its core-sampling position in the outer barrel, so as to lock the free end element on the end portion in another extreme position situated beyond the said contact position starting from the extreme position away from the internal surface.
Other details and particular features of the invention will emerge from the secondary claims and from the description of the drawings which are appended to this text and which illustrate, by way of non-limiting examples, some embodiments of the invention.